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2.7.7
Program-Counter Relative—@(d:8, PC) or @(d:16, PC)
This mode can be used by the Bcc and BSR instructions. An 8-bit or 16-bit displacement
contained in the instruction code is sign-extended to 24 bits and added to the 24-bit address
indicated by the PC value to generate a 24-bit branch address. Only the lower 24 bits of this
branch address are valid; the upper 8 bits are all assumed to be 0 (H'00). The PC value to which
the displacement is added is the address of the first byte of the next instruction, so the possible
branching range is –126 to +128 bytes (–63 to +64 words) or –32766 to +32768 bytes (–16383 to
+16384 words) from the branch instruction. The resulting value should be an even number.
2.7.8
Memory Indirect—@@aa:8
This mode can be used by the JMP and JSR instructions. The instruction code contains an 8-bit
absolute address specifying a memory operand which contains a branch address. The upper bits of
the 8-bit absolute address are all assumed to be 0, so the address range is 0 to 255 (H'0000 to
H'00FF in normal mode, H'000000 to H'0000FF in advanced mode).
In normal mode, the memory operand is a word operand and the branch address is 16 bits long. In
advanced mode, the memory operand is a longword operand, the first byte of which is assumed to
be 0 (H'00).
Note that the top area of the address range in which the branch address is stored is also used for
the exception vector area. For further details, see section 4, Exception Handling.
If an odd address is specified in word or longword memory access, or as a branch address, the
least significant bit is regarded as 0, causing data to be accessed or the instruction code to be
fetched at the address preceding the specified address. (For further information, see section 2.5.2,
Memory Data Formats.)
Specified
by @aa:8
Figure 2.12 Branch Address Specification in Memory Indirect Addressing Mode
Branch address
(a) Normal Mode
Specified
Reserved
by @aa:8
Branch address
(b) Advanced Mode
Rev. 3.00 Jan 25, 2006 page 47 of 872
Section 2 CPU
REJ09B0286-0300
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